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 A023814 Number of associative binary operations on an n-set; number of labeled semigroups. 14
 1, 1, 8, 113, 3492, 183732, 17061118, 7743056064, 148195347518186, 38447365355811944462 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Alex Bailey, Martin Finn-Sell, Robert Snocken, Subsemigroup, ideal and congruence growth of free semigroups, arXiv preprint arXiv:1409.2444, 2014. A. Distler and T. Kelsey, The semigroups of order 9 and their automorphism groups, arXiv preprint arXiv:1301.6023, 2013. C. Noebauer, Home page [broken link] C. Noebauer, The Numbers of Small Rings C. Noebauer, Thesis on the enumeration of near-rings Eric Postpischil Posting to sci.math newsgroup, May 21 1990 Eric Weisstein's World of Mathematics, Semigroup. CROSSREFS Cf. A001423, A001426, A023813, A023815, A027851. a(n) + A079172(n) = A002489(n). Sequence in context: A072402 A092084 A099715 * A217772 A062126 A222520 Adjacent sequences:  A023811 A023812 A023813 * A023815 A023816 A023817 KEYWORD nonn AUTHOR Lyle Ramshaw (ramshaw(AT)pa.dec.com) EXTENSIONS a(8), a(9) from Distler and Kelsey (2013). - N. J. A. Sloane, Feb 19 2013 STATUS approved

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Last modified December 12 19:33 EST 2018. Contains 318081 sequences. (Running on oeis4.)